Explanation:

In order to write the equilibrium constant expression we have to form a quotient where numerator contains the concentrations of the substance on product side of the equilibrium equation,each raised to a power equal to its coefficient in the balanced equatiopn . The denominator is similarly obtained using the substances on the reactant side of the equation :

Kc = [ O_{2}]^{3} / [ O_{3}]^{2}

Answer:

Kc = [ O_{2}]^{3} / [ O_{3}]^{2}